Method of conducting reservoir pilot tests with a single well



Dec. 29, 1964 D. H. HENLl-:Y

METEOO OF OONOUOTTNG RESERVOIR PILOT TESTS WITH A SINGLE wELL 5 Sheets-Sheet 1 Filed June 5, 1961 FIGURE DONALD H. HENLEY INVENTOR.

BY f

ATTORNEY.

Dec. 29, 1964 D. H. HENLE 3,163,211

METHOD OF CONDUC TING RES OIR PILOT TESTS WITH A SINGLE WELL Filed June 5. 1961 5 Sheets-Sheet 2 FIGURE-2 DONALD H, HENLEY IN VEN TOR.

` ATTORNEY Dec. 29, 1964 D. H. HENLEY METHOD OF CONDUCTING RESERVOIR PILOT TESTS WITH A SINGLE WELL 5 Sheets-Sheet i5 Filed June 5. 1961 FIGURE-3 DONALD H. HENLEY INVENTOR. 12x/M` )7l @2&7

ATTORNEY Dec. 29, 1964 D. H. HENLEY 3,163,211

METHOD OF CONDUCTING RESERVOIR PILOT TESTS WITH A SINGLE WELL Filed June 5. 1961 5 Sheets-Sheet `4 DONALD H. HENLEY INVEN TOR.

BY Mwmld? ATTORNEY.

Dec. 29, 1964 Filed June 5, 1961 D. H. HENLEY 3,163,211 METHOD OF' CONDUCTING RESERVOIR PILOT TESTS WITH A SINGLE WELL 5 Sheets-Sheet 5 FIGURE-5 DONALD H. HENLEY INVENTOR.

BYMMQ 17 ATTORNEY United States Patent 3,163,211 METHOD F CQNDUCTlNG RESERVlR PILOT TESTS WITH A SKNGLE WELL Donald H. Henley, Tulsa, Ukla., assigner to Pan American Petroleum Corporation, Tulsa, Okla., a corporation of Delaware Filed June 5, 1961, Ser. No. 114,987 14 Claims. (Cl. 166-4) The present invention relates to the production of petroleum from subterranean reservoirs by means of secondary recovery methods. More particularly, it is concerned with a method for testing and determining the characteristics of a reservoir such as, for example, the homogeneity or floodability of said reservoir, by the use of a single pilot or test well.

Briefly, one embodiment of my invention involves placing a packer at an intermediate level in the formation to be tested so as to form an essentially fluid-tight seal in the well between the zones above and below the packer. Thereafter, test fluid is introduced into one of said zones, produced into the well via the other, and recovered. In carrying out such a test, the packer may be placed between perforations in a cased well or a sealant may be placed in an open hole section, and that portion of the formation covered by sealant confined by .a packer 'at either end thereof. Such sealing step may, if desired, be accomplished by using an oil base mud, for example, to seal olf the zone defined by the packers. Fluid is then injected into the formation, for example, above the upper packer, permitted to flow into the well below Vthe bottom packer, and then produced via tubing through said packers. Alternatively, injection of fluid into the formation may be beneath the lower packer, particularly if a duid heavier than oil is used, and produced into the well above the upper packer.

In still another embodiment of my invention, the producing formation is notched or underreamed at a level nearv the base thereof, and thereafter a substantially horizontal fracture is formed out through the formation from the resul-ting notch. A second notch and fracture are similarly placed at a level near the top of the producing formation. Between these two fractures there is placed a packer on production tubing. If the well is uncased between the fractures, the formation face should be sealed off. Fluid, which may be the same as used in forming the fractures, is then introduced into the upper fracture. The lluid Vthus introduced which, for example, is lighter than the oil in the reservoir, flows back into the formation and eventually forces hydrocarbons out of the reservoir and into the well via the lower fracture. Injection of uid through the upper fracture is continued, while hydrocarbons are produced through the lower fracture. In this way, in a relatively short time, for example thirty to forty days, the behavior of a fluid drive agent in a given reservoir can be determined. While frac-tures are not necessarily essential in. carrying out the `process of my invention, they provide higher injectivity and shorter test periods. Also, they increase the possibility of increasing the volume of reservoir contacted.

In the drawings, FlGUREl represents an oil-producing formation penetrated by a cased well wherein fractures lhave been made at levels near the top and bottom of said formation.

the formation. y

FIGURE 3 shows a cross-section of the same system as illustrated in FIGURE 2 at a later stage in the process.

FIGURE 4 illus-trates still another embodiment of my invention wherein the flooding fluid, which is heavier than ice the, oil to be produced, is injected into the lowermost of two fractures in a formation penetrated by an open hole.

FIGURE 5 is a vertical sectional view illustrating a plication of the principles of my invention in determining directional permeability of the reservoir. n

In any secondary recovery process, preliminary studies of the reservoir to be flooded must be made in order to establish the flooding sys-tem -that will yield the highest recovery. Ideally, it would be desirable to make such 'studies under conditions identical with those prevailing inl the reservoir. However, in the past this has not been possible. Usually, the reservoir characteristics were best determined by taking a core of the formation under investigation, forcing certain lluids through it and, from the results thus obtained, arriving at allooding system considered most suitable for the recovery operation contemplated. One chief difficulty with core studies, however, is that it is practically impossible to obtain a core having properties identical to the reservoir Vrock in its natural state.V This is true because in obtaining such a core its permeability/,is altered to some extent by the drilling mud contacting it during the coring operation. Also, it is impossible to determine from a core such gross reservoir characteristics as directional permeability, since theV small core sample may not be representative of larger portions of the reservoirA Ordinarily when a secondary recovery operation of the fabove mentioned type is planned, and after all information has been obtained lthat can be secured by means of coretes-ts, a pilot ilood involving usually not more than 4 or 5` acres is initiated. Even with such a small scale test it is generally at least a year before the'information necessary for successful performance of the main secondary recovery operation can be obtained. Such an extended period for the procurement of preliminary information not only is expensive to conduct, but the results may indicate a large-scale flood is not feasible; in which case valuable time has been wasted in pursuing an unprofitable project.

One of the outstanding advantages of the process of my invention is that valuable information of the type required to ascertain whether large-scale flooding opera- Y tions should be conductedV can be, determined under natural reservoir conditions within a relatively short tune. Avery desirable featureresulting from being able to study the reservoir under natural conditions is that I am not only able to determine its horizontal and vertical permeability,but it is also possible to ascertain the directional permeability of the reservoir as well. rl`he latter characteristic is extremely important in any secondary recovery operation. Thus, if 'injection of the flooding agent is conducted under conditions such that said agent travels through the reservoir in the direction of greatestpermeability, early breakthrough of said agent occurs, causing poor recovery. On the other hand, if the flooding agent is'injected in such a way so that it tends to follow .a path essentially perpendicular to the direction of greatest permeability, breakthrough of the flooding agent is delayed, resulting in good sweep etliciency which, in turn, makes possible good'oil recovery.

By operating in accordance with the procedure of my invention, the flooding agent is able to contact a large area in the .vicinity of .the weil in a short time. By monitoring the composition of the produced stream, in-

` formation is provided from which an evalution of forma-l tion properties can be made. For instance, if it is` desired to introduce an additive into the flooding agent,

,say for the purpose of effecting a change in wettability characteristics of the reservoir rock, one must know whether or not such additive tends to be adsorbed onto the rock when contacted by the ilooding agent. Accordvrin :the uncased section between the packers. injection of water into fracture 18 results in forcing-1 theA oilin the formation upwardly toward fracture; 16 and established.

The method of my invention will be further illustrated by reference to FIGURES l to5, in which' a well equipped with casing 2 is secured in any oil-bearing formatlon 4 by means of cement 5, or other suitable securing agent. At

levels Vnear thebottom and top lof said formation, the casing is cut in any known manner, such as by jettmg After the casing is cut, the cement and formation back vof the casing isknotched vor underreamed either by the use of abrasive fluids, or by use of a suitable tool; at 12 and 14.

' Y These notches create zones of weakness which, when the formation is subjected to Vhydraulic fracturing at such levels, tend to produce horizontal fractures 16 and 18.

In formingfractures at 18, suitable props 20 may be present in the fracturing liquid in ord'erto .provide flow capacity. During the fracturing step the fluid 1s 1njected Vinto-the conlinedzone formed by packer v2.2, and

the bottom vof the well. Fracturev -16 may either Ybe propped open in the same manner,`or the same result can be obtained if high injection rates'are maintained. The fracturing fluid, if injected at 16', should eitherbe composed of a fluid lighterthan theereservoir oil,'or should comprise a slug of low-penetrating materialfollowed :by the light fracturing uid if losses of the-latter to theformation tend to prevent a large-radius fracturei Test fluid or'ilooding agent, which may be LPG, gas, etc;,isV forced through tubing 24 and into fracture 16 at a rate such that it is held open. Introduction of the flooding agent is confined to the-zone` defined by packers 22 and 26. When flooding agent is injected, it flows into the formation in a pattern 30, the nature of which depends upon the characteristics of the reservoir andof the injected fluid.. During this step tubing 25 is permitted to remainopen so kas to create a substantial pressure drop across the formation face at notch 14, thereby aiding in forcing said agent out of theformation and `into the wellbore. FIGURE 3 shows a later stage of the process in which the llooding agent and reservoir fluids are V`ultimately producedinto the wellbore via fracture 18. The resultingmixture is removed from the well via tubing 25, and the cor'rno'sitionV requires proper sealing of the formation face Vbetween packers 22 and V26. yThis can beaccomplished by filling 'sand-laden oil against the metal surface at 9 and 10. y.

conrtinued until the water-oil ratio has increased to a maximum .realistic level.

As previously mentioned, one of the more valuable kinds of information afforded by the process of my invention is concerned withdetermining directional permeability of reservoir under investigation. Thus, in establishing. this characteristic of a given reservoir,-perforations are first made at positions 34 and 36, as shown'in FIG- URE 5, with packer 22 separating the two sets. These Y may consist of more than one perforation, preferably arranged vertically, at each of the designated positions. After the desired numbenof suchperforations have been made, fluid, such as, for example, LPG, is injected lthrough the perforation or perforations 34 and intotbe formation. In place of LPG,.reservoir oil, if desired, may be substituted to assure that the saturation around the well will vremain constant. YThe time required Afor breakthrough of LPG and thercomposition and volume of fluid produced through tubing V25 over a given time interval after said breakthrough are then measured. Next, perforations 34 Y -and 36 are sealed olf by any of several known methods. For example, the upper set of perforations 34 Vcould'be closed by the-use of ball Sealers, while thelower set could be sealedv olf by spotting a small amount of plastic opposite perforations 36 and forcing said plastic therein. After perforations VIland 36'are adequately blanked off, additional perforations may be made-in the casing about 90 from the alignment of groups 34 and 36. Thereafter, in-

. ered necessary or desirable, the above-mentioned proced-V jection tests are vmade vin the same manner asy described in connection withperforations 34 and 36. `By establishing the time required for breakthrough of LPG, and `the composition and Vvoliune .of-produced fluid over a given period, such results can becomparedwith those obtained in the first phase of the process in order to establish the j i v junction with other reservoir fluid properties in the two and sealing thezone between the two packers `with oil base mud- 32, or other similar material.V The oil base mud usedto seal the formation face should bernaintained at a pressure in excess of the injection pressure of the test fluid into the formation. This will insure a positive seal Continued into the open hole via fracture 16 above packer 26, where it is produced through tubing 24. Eventually, a breakthrough of water or other similar flooding agent intothe well via fracture 16 occurs.V Injection of said agent is directions apart, are a measure ofthe directional permeability difference. Actually, directional permeability can be established without using a material such as LPG or water. .In other words, such characteristic can be determined .without observing the time required for breakthrough. Thus, crude oilY may be .used as theinjection` fluid, in which casethe pressure drop andiiow ratenof `said iuid can be used as indicators of such permeability.

`Alternatively, directional permeability of a reservoir,

Vparticularly where the reservoir is `of substantial thickness,

eg., 50 to 100 feet, can be determined in accordance with my inventionv by `first setting a packer between two groups l of perforations and .thereafter Vcarrying out the injection test as described above; The perforations for the second phase of the test maythen be placed (at least'about 90@ away from the former) several feet, eg., l5 to 20 feet,.

cases, the orientation of the perforations shouldbe dif` ferent from that employed before, in order to obtain the maximum Vamount of information.

A further variation also contemplated by my invention involves the making of several pairs of perforations, each group of a pair being separated by a packer or equivalent during the test-throughout the thickness of the producing formationY if desired. By conducting injection tests with In addition to using each pair of perforations throughout the thickness of said formation, important information concerning the characteristics thereof such as, for example, the presence of shale streaks, etc., can be determined.

By the term cased well, as used in the present descn'ption and claims, I intend to include both cased Wells and wells having an open hole section opposite the formation under test. or investigation. InV such open hole section, however, it is to be understood that no direct communication between fractures or perforations via the well is possible.

The fracturing fluids employed in carrying out the process of my invention may vary widely. As examples of such materials there may be mentioned gas, water, water containing agents to alter the natural wettability of the reservoir, light hydrocarbons in liquid or gaseous form such as propane, butane or pentane, or mixtures thereof, for example, LPG.

I claim: l

l. In a method for obtaining information on a hydrocarbon-containing formation traversed by a well pnior to subjecting said formation to a procedure in which a Huid is to be injected into said formation, the'v improvement which comprises:

penetrating said formation at a level near the top thereof and at a level near the bottom ofl said formation,

placing a substantially fluid-tight barrier in said well between said penetrated levels,

injecting a test fluid into one of said levels,

permitting said fluid to be produced into said Well via the lother of said penetrated levels, determining the time required for said injected test v fluid to break thnough said formation and into said well,

recoveringthe uids thus produced including said testv Huid, measuring the flow rate and pressure drop of the injected test iiuid across said formation,

monitoring the composition and volume of said fluids produced into said well during said injection step; and thereafter, on the basis of the information thus obtained, injecting said fluid into said formation via a well (i) penetrating said formation and recovering hydrocarbon-containing fluids from a second well spaced apart from well (1) and, likewise, extending into said formation.

2. in a method for obtaining information on a hydrocarbon-containing formation traversed by a well prior to subjecting said formation to a procedure in which a fluid is to be injected into said formation, the improvement which comprises:

fracturing said formation at a level near the top thereof and at a level near the bottom of said formation, placing a substantially fluid-tight barrier in said well between said fractured levels,

injecting a test fluid into one of said levels,

permitting said huid to be produced into said well via the other of said fractured levels,

determining the time required for said injected test uild to break through said formation and into said we l,

measuring the flow rate and pressure drop of the injected test fluid across said formation,

recovering the fluids thus produced,

monitoring the composition and volume of said fluids produced intoV said'well during said-injection step; and thereafter, on the basis of the information thus obtained, injecting said iiuid into said formation via a well (1) penetrating said formation and recovering hydrocarbon-containing uids from a second well spaced apart from well (1) and, likewise, extending into said formation.

3. rIlhe method of claim 2 in which the injected uid is lighter than the petroleum in said reservoir and said formation.y

4. The method of claim 3 in which the injected fluid is l. j

a hydrocarbon in liquid form when injected.

5. The method of claim 2 wherein the injected fluid is heavier than the liquid hydrocarbons in said formation and said uid is injected into the fracture near the bottom of said formation.

6. The method of claim 5 in which the injected fluid is water.

7.` In a method for obtaining information on a formation containing liquid hydrocarbons penetrated by a cased well prior to subjecting said formation to a procedure in which a Huid is to be injected into said formation, the impnovement which comprises:

cutting said casing at a level near the top` of said formation and at a level near the bottom thereof, forming a substantially horizontal notch in said formation at the location of each of said levels, fr-acturing said formation at said levels,

placing a packer in said casingrbetween said notches,

injecting a test iiuid lighter than said liquid hydrocarbons into said formation via the uppermost of :said fractures, permitting said test fluid to be produced into saidV well via the other of said fractures, Y determining the time required for said injected iiuid to break through said formation and into said well, measuring the ilow rate and pressure ldrop of the injected test duid across said formation, recovering the uids thus produced including said test fluid While continuing the injection of said uid into said uppermost fracture,

monitoring the composition and volume of said fluids produced into said well during said injection step; and thereafter, on the basis of the information thus obtained, injecting said iluid into said formation via a well (1) penetrating said formation and recovering hydrocarbon-containing iuids from'. a second well spaced apart from well (1) and, likewise, extending into said formation.

8. In a method for determining the directional permeability of a liquid hydrocarbon-containing formation traversed by a cased well prior to subjecting said formation to a pnocedure in which a fluid is to be injected into said formation, the improvement which comprises:

penetrating said formation at levels near the top and near the bottom thereof, said penetrating step being carried out so as to produce perforations in said formation at both of said levels and in a common, substantially horizontally oriented path,

placing a substantially huid-tight barrier -in said well between said penetrated levels,

injecting a fluid into one of said penetrated levels, producing formation fluids into said well via the other` of said penetrated levels,

monitoring the volume of said iluids produced into said well during said injection step,`

determining the pressure drop required to achieve a measured flow rate,

thereafter again penetrating said formation at a level near the top thereof .and at a level near the bottom of said formation, said` last-mentioned perforating step being carried out at both of said levels so as to produce perforations in said formation in a common, substantially horizontally oriented path but different f nom` the direction of the first-mentioned set of perforations,

injecting a fluid into one of said last-mentioned perforations, Y producing said injection Viiuid and formation fluids, including liquid hydrocarbons, into said well via the other of said last-mentioned perforations, monitoring the volume of said fluids produced into said well via said other of said last-mentioned per- 7, foratifons during said injection step, and

determining the pressure drop required to achieve a measured 110W rate.V Y

9. The method of claim V8 inwhich the injection uid is lighter than said liquid hydrocarbons, and is injected into the perforations near the topof said formation.

10. In a method for obtaining information on a liquid hydrocarbon-containing formadon traversed by a weil prior to subjecting said formation to a' procedure in which Y a fluid is to be injected into said formation, theimprovement which vcomprises: l Y

sealing oif the face of a i section of saidweil in said formation, Y setting production packers at both'ends of said sealedoff portion whereby :no communication via said well is possible between said packers, Y l

yportion of an open hole injecting a fluid into said formation at one of said ends, y

producing formation uids into said wel] via the other of said ends, Y

Vmeasuring the fiow rate and pressure drop Vof therin-V jected fiuid across said formation, Y recovering the fiuids thus produced, V monitoring the volume rof said fluids produced into l saidweliduring said injection step; 'and thereafter,

`on the basisV of the information `thus obtained, in-

subjecting said formation to a procedure in which a Huid Y is to be injected into said formation, the improvement which comprises: Y Y i i penetrating ysaid formation at a level `near the top thereof and at a level near the bottom of said formation, Y i Y placing za substantiallyV Ihuid-tight barrier in said Well between said penetrated levels,

whichthe Viuid injected fluid injected 8 f -*injecting a' tcstiftuidinto one of said 1evels, permitting-'said fluid to be produced into said weil via the other of saidV penetrated levels,

determining the time-required forsaid-injected test'- -Y prior to subjecting said formation to a procedure in which a fluid is to be injected int-o said formation, the improvement which comprises: v

sealing off the face of a portion of'anop'en hole section of said well in said formation, setting pnoduction packersv at both ends of said sealedj -otf portion whereby no communication via said is possible betweenesaid packers, injecting afluidinto said formation at one of said ends, producing formation iuids into said weil via the other `lof said ends, measuring the fiow rate and pressure drop of the injected fluid across said formation, recovering the fluids thus produced, and monitorin lche volume of said'uids produced into said well during said inection step. Y

2,593,497 sp'eafow -2 Apr. 22,

l 2,742,089; Morse et al. Apr. 17, 1956 2,754,911 Speanow ,Tuly 17,1956 2,758,653 yDesbrow Aug. 14, 1956 2,821,255 Spearow Ian. 28, 1958 2,852,556 Frek 2-2----,2 Dec. 2, `195s Y OTHER REFERENCES Amyx, I. W.

, et alf: Petroleum Reservoir Engineering,

McGraw-Hill, 1960, pages 4781-488. 

1. IN A METHOD FOR OBTAINING INFORMATION ON A HYDROCARBON-CONTAINING FORMATION TRAVERSED BY A WELL PRIOR TO SUBJECTING SAID FORMATION TO A PROCEDURE IN WHICH A FLUID IS TO BE INJECTED INTO SAID FORMATION, THE IMPROVEMENT WHICH COMPRISES: PENETRATING SAID FORMATION AT A LEVEL NEAR THE TOP THEREOF AND AT A LEVEL NEAR THE BOTTOM OF SAID FORMATION, PLACING A SUBSTANTIALLY FLUID-TIGHT BARRIER IN SAID WELL BETWEEN SAID PENETRATED LEVELS, INJECTING A TEST FLUID INTO ONE OF SAID LEVELS, PERMITTING SAID FLUID TO BE PRODUCED INTO SAID WELL VIA THE OTHER OF SAID PENETRATED LEVELS, DETERMINING THE TIME REQUIRED FOR SAID INJECTED TEST FLUID TO BREAK THROUGH SAID FORMATION AND INTO SAID WELL, RECOVERING THE FLUIDS THUS PRODUCED INCLUDING SAID TEST FLUID, MEASURING THE FLOW RATE AND PRESSURE DROP OF THE INJECTED TEST FLUID ACROSS SAID FORMATION, MONITORING THE COMPOSITION AND VOLUME OF SAID FLUIDS PRODUCED INTO SAID WELL DURING SAID INJECTION STEP; AND THEREAFTER, ON THE BASIS OF THE INFORMATION THUS OBTAINED, INJECTING SAID FLUID INTO SAID FORMATION VIA A WELL (1) PENETRATING SAID FORMATION AND RECOVERING HYDROCARBON-CONTAINING FLUIDS FROM A SECOND WELL SPACED APART FROM WELL (1) AND, LIKEWISE, EXTENDING INTO SAID FORMATION. 